Elements of Structural and Systematic Botany Part 1

Elements of Structural and Systematic Botany.

by Douglas Houghton Campbell.

PREFACE.

The rapid advances made in the science of botany within the last few years necessitate changes in the text books in use as well as in methods of teaching. Having, in his own experience as a teacher, felt the need of a book different from any now in use, the author has prepared the present volume with a hope that it may serve the purpose for which it is intended; viz., an introduction to the study of botany for use in high schools especially, but sufficiently comprehensive to serve also as a beginning book in most colleges.

It does not pretend to be a complete treatise of the whole science, and this, it is hoped, will be sufficient apology for the absence from its pages of many important subjects, especially physiological topics.

It was found impracticable to compress within the limits of a book of moderate size anything like a thorough discussion of even the most important topics of _all_ the departments of botany. As a thorough understanding of the structure of any organism forms the basis of all further intelligent study of the same, it has seemed to the author proper to emphasize this feature in the present work, which is professedly an _introduction_, only, to the science.

This structural work has been supplemented by so much cla.s.sification as will serve to make clear the relationships of different groups, and the principles upon which the cla.s.sification is based, as well as enable the student to recognize the commoner types of the different groups as they are met with. The aim of this book is not, however, merely the identification of plants. We wish here to enter a strong protest against the only too prevalent idea that the chief aim of botany is the ability to run down a plant by means of an "a.n.a.lytical Key," the subject being exhausted as soon as the name of the plant is discovered. A knowledge of the plant itself is far more important than its name, however desirable it may be to know the latter.

In selecting the plants employed as examples of the different groups, such were chosen, as far as possible, as are everywhere common. Of course this was not always possible, as some important forms, _e.g._ the red and brown seaweeds, are necessarily not always readily procurable by all students, but it will be found that the great majority of the forms used, or closely related ones, are within the reach of nearly all students; and such directions are given for collecting and preserving them as will make it possible even for those in the larger cities to supply themselves with the necessary materials. Such directions, too, for the manipulation and examination of specimens are given as will make the book, it is hoped, a laboratory guide as well as a manual of cla.s.sification. Indeed, it is primarily intended that the book should so serve as a help in the study of the actual specimens.

Although much can be done in the study, even of the lowest plants, without microscopic aid other than a hand lens, for a thorough understanding of the structure of any plant a good compound microscope is indispensable, and wherever it is possible the student should be provided with such an instrument, to use this book to the best advantage. As, however, many are not able to have the use of a microscope, the gross anatomy of all the forms described has been carefully treated for the especial benefit of such students. Such portions of the text, as well as the general discussions, are printed in ordinary type, while the minute anatomy, and all points requiring microscopic aid, are discussed in separate paragraphs printed in smaller type.

The drawings, with very few exceptions, which are duly credited, were drawn from nature by the author, and nearly all expressly for this work.

A list of the most useful books of reference is appended, all of which have been more or less consulted in the preparation of the following pages.

The cla.s.sification adopted is, with slight changes, that given in Goebel's "Outlines of Morphology and Cla.s.sification"; while, perhaps, not in all respects entirely satisfactory, it seems to represent more nearly than any other our present knowledge of the subject. Certain groups, like the Diatoms and _Characeae_, are puzzles to the botanist, and at present it is impossible to give them more than a provisional place in the system.

If this volume serves to give the student some comprehension of the real aims of botanical science, and its claims to be something more than the "a.n.a.lysis" of flowers, it will have fulfilled its mission.

DOUGLAS H. CAMPBELL.

BLOOMINGTON, INDIANA, October, 1889.

BOTANY.

CHAPTER I.

INTRODUCTION.

All matter is composed of certain const.i.tuents (about seventy are at present known), which, so far as the chemist is concerned, are indivisible, and are known as elements.

Of the innumerable combinations of these elements, two general cla.s.ses may be recognized, organic and inorganic bodies. While it is impossible, owing to the dependence of all organized matter upon inorganic matter, to give an absolute definition, we at once recognize the peculiarities of organic or living bodies as distinguished from inorganic or non-living ones. All living bodies feed, grow, and reproduce, these acts being the result of the action of forces resident within the organism. Inorganic bodies, on the other hand, remain, as a rule, unchanged so long as they are not acted upon by external forces.

All living organisms are dependent for existence upon inorganic matter, and sooner or later return these elements to the sources whence they came. Thus, a plant extracts from the earth and air certain inorganic compounds which are converted by the activity of the plant into a part of its own substance, becoming thus incorporated into a living organism. After the plant dies, however, it undergoes decomposition, and the elements are returned again to the earth and atmosphere from which they were taken.

Investigation has shown that living bodies contain comparatively few elements, but these are combined into extraordinarily complex compounds. The following elements appear to be essential to all living bodies: carbon, hydrogen, oxygen, nitrogen, sulphur, pota.s.sium.

Besides these there are several others usually present, but not apparently essential to all organisms. These include phosphorus, iron, calcium, sodium, magnesium, chlorine, silicon.

As we examine more closely the structure and functions of organic bodies, an extraordinary uniformity is apparent in all of them. This is disguised in the more specialized forms, but in the simpler ones is very apparent. Owing to this any attempt to separate absolutely the animal and vegetable kingdoms proves futile.

The science that treats of living things, irrespective of the distinction between plant and animal, is called "Biology," but for many purposes it is desirable to recognize the distinctions, making two departments of Biology,--Botany, treating of plants; and Zoology, of animals. It is with the first of these only that we shall concern ourselves here.

When one takes up a plant his attention is naturally first drawn to its general appearance and structure, whether it is a complicated one like one of the flowering plants, or some humbler member of the vegetable kingdom,--a moss, seaweed, toadstool,--or even some still simpler plant like a mould, or the apparently structureless green sc.u.m that floats on a stagnant pond. In any case the impulse is to investigate the form and structure as far as the means at one's disposal will permit. Such a study of structure const.i.tutes "Morphology," which includes two departments,--gross anatomy, or a general study of the parts; and minute anatomy, or "Histology," in which a microscopic examination is made of the structure of the different parts. A special department of Morphology called "Embryology" is often recognized. This embraces a study of the development of the organism from its earliest stage, and also the development of its different members.

From a study of the structure of organisms we get a clue to their relationships, and upon the basis of such relationships are enabled to cla.s.sify them or unite them into groups so as to indicate the degree to which they are related. This const.i.tutes the division of Botany usually known as Cla.s.sification or "Systematic Botany."

Finally, we may study the functions or workings of an organism: how it feeds, breathes, moves, reproduces. This is "Physiology," and like cla.s.sification must be preceded by a knowledge of the structures concerned.

For the study of the gross anatomy of plants the following articles will be found of great a.s.sistance: 1. a sharp knife, and for more delicate tissues, a razor; 2. a pair of small, fine-pointed scissors; 3. a pair of mounted needles (these can be made by forcing ordinary sewing needles into handles of pine or other soft wood); 4. a hand lens; 5. drawing-paper and pencil, and a note book.

For the study of the lower plants, as well as the histology of the higher ones, a compound microscope is indispensable. Instruments with lenses magnifying from about 20 to 500 diameters can be had at a cost varying from about $20 to $30, and are sufficient for any ordinary investigations.

Objects to be studied with the compound microscope are usually examined by transmitted light, and must be transparent enough to allow the light to pa.s.s through. The objects are placed upon small gla.s.s slips (slides), manufactured for the purpose, and covered with extremely thin plates of gla.s.s, also specially made. If the body to be examined is a large one, thin slices or sections must be made. This for most purposes may be done with an ordinary razor. Most plant tissues are best examined ordinarily in water, though of course specimens so mounted cannot be preserved for any length of time.[1]

[1] For the mounting of permanent preparations, see Chapter XIX.

In addition to the implements used in studying the gross anatomy, the following will be found useful in histological work: 1. a small camel's-hair brush for picking up small sections and putting water in the slides; 2. small forceps for handling delicate objects; 3.

blotting paper for removing superfluous water from the slides and drawing fluids under the cover gla.s.s; 4. pieces of elder or sunflower pith, for holding small objects while making sections.

In addition to these implements, a few reagents may be recommended for the simpler histological work. The most important of these are alcohol, glycerine, potash (a strong solution of pota.s.sium hydrate in water), iodine (either a little of the commercial tincture of iodine in water, or, better, a solution of iodine in iodide of pota.s.sium), acetic acid, and some staining fluid. (An aqueous or alcoholic solution of gentian violet or methyl violet is one of the best.)

A careful record should be kept by the student of all work done, both by means of written notes and drawings. For most purposes pencil drawings are most convenient, and these should be made with a moderately soft pencil on unruled paper. If it is desired to make the drawings with ink, a careful outline should first be made with a hard pencil and this inked over with India-ink or black drawing ink. Ink drawings are best made upon light bristol board with a hard, smooth-finished surface.

When obtainable, the student will do best to work with freshly gathered specimens; but as these are not always to be had when wanted, a few words about gathering and preserving material may be of service.

Most of the lower green plants (_algae_) may be kept for a long time in gla.s.s jars or other vessels, provided care is taken to remove all dead specimens at first and to renew the water from time to time. They usually thrive best in a north window where they get little or no direct sunshine, and it is well to avoid keeping them too warm.

Numbers of the most valuable fungi--_i.e._ the lower plants that are not green--grow spontaneously on many organic substances that are kept warm and moist. Fresh bread kept moist and covered with a gla.s.s will in a short time produce a varied crop of moulds, and fresh horse manure kept in the same way serves to support a still greater number of fungi.

Mosses, ferns, etc., can be raised with a little care, and of course very many flowering plants are readily grown in pots.

Most of the smaller parasitic fungi (rusts, mildews, etc.) may be kept dry for any length of time, and on moistening with a weak solution of caustic potash will serve nearly as well as freshly gathered specimens for most purposes.

When it is desired to preserve as perfectly as possible the more delicate plant structures for future study, strong alcohol is the best and most convenient preserving agent. Except for loss of color it preserves nearly all plant tissues perfectly.

CHAPTER II.

THE CELL.

If we make a thin slice across the stem of a rapidly growing plant,--_e.g._ geranium, begonia, celery,--mount it in water, and examine it microscopically, it will be found to be made up of numerous cavities or chambers separated by delicate part.i.tions. Often these cavities are of sufficient size to be visible to the naked eye, and examined with a hand lens the section appears like a piece of fine lace, each mesh being one of the chambers visible when more strongly magnified. These chambers are known as "cells," and of them the whole plant is built up.

[Ill.u.s.tration: FIG. 1.--A single cell from a hair on the stamen of the common spiderwort (_Tradescantia_), 150. _pr._ protoplasm; _w_, cell wall; _n_, nucleus.]

In order to study the structure of the cell more exactly we will select such as may be examined without cutting them. A good example is furnished by the common spiderwort (Fig. 1). Attached to the base of the stamens (Fig. 85, _B_) are delicate hairs composed of chains of cells, which may be examined alive by carefully removing a stamen and placing it in a drop of water under a cover gla.s.s. Each cell (Fig. 1) is an oblong sac, with a delicate colorless wall which chemical tests show to be composed of cellulose, a substance closely resembling starch. Within this sac, and forming a lining to it, is a thin layer of colorless matter containing many fine granules.